(1) Field of the Invention
The present invention relates to a technique for preventing inauthentic alterations of battery packs for use in portable electronic equipment.
(2) Description of Related Art
The power consumption of portable electronic equipment is rising. For example, the power consumption of notebook personal computers typically rises each year, driven in part by increases in central processing unit (CPU) operating frequency. As used herein, notebook personal computers are referred to as notebook PCs. To accommodate the need for increased power, a demand for reduced battery size and weight, and other needs, notebook PCs have begun using lithium ion batteries and nickel hydrogen batteries with higher energy density in place of conventional nickel-cadmium batteries. At the same time, a battery mechanism called a Smart Battery has become commonly accepted. With the Smart Battery, a battery pack itself contains a microcomputer and controls charging and discharging by exchanging information with the notebook PC itself, to use a battery pack efficiently by strictly managing charge/discharge state. The Smart Battery is battery equipment compliant with the Smart Battery System (SBS) proposed by Intel Corporation of Santa Clara, Calif., and Duracell Inc. of Bethel, Conn. Battery packs that comply with the SBS standard are also referred to as intelligent batteries.
A battery pack that meets SBS intelligent battery requirements consists of an electric circuit portion which in turn consists of a battery block made up of a combination of multiple cells, a CPU, a current measurement circuit, a voltage measurement circuit, various sensors, and the like, all mounted on a substrate. The CPU communicates with an embedded controller in the body of the notebook PC via a communications line and manages charging and discharging between the cells and notebook PC body, making it possible to maintain stable discharging for a long period of time. Also the notebook PC can change power consumption modes according to a cells' remaining capacity or stop operation after presenting a warning on a display if the remaining capacity falls.
Lithium ion batteries are at high risk of ignition, fuming, bursting, performance degradation, and the like in case of overcharge or overdischarge. Thus, the electric circuit of the intelligent battery prevents overcharge by shutting off charge current when cell voltage becomes equal to or higher than a full-charge voltage. The intelligent battery also prevents overdischarge by shutting off discharge current when cell voltage becomes equal to or lower than a discharge inhibit voltage. Also, when an overcurrent occurs, the electric circuit prevents degradation of the cells and breakage of the electric circuit by shutting off current. Once the full-charge voltage, discharge inhibit voltage, or overcurrent conditions are corrected, the intelligent battery can be used normally again.
A battery block is generally made up of a combination of multiple battery cells such as a two-in-parallel and three-in-series combination in order to provide the voltage required for operation of the notebook PC and to extend operating time on the battery pack. When multiple cells are connected in parallel, if two or more cells differ in electric potential are connected in parallel, an intercell current flows. The intercell current depends on a potential difference between the cells and on internal resistance of the cells. Since the internal resistance of the cells is very low, when cells are connected in parallel, even a slight potential difference between the cells will cause a large intercell current to flow into the cell, which in turn may cause burnout of circuit elements or degradation of cells.
Physical properties such as full-charge voltage, discharge inhibit voltage, and potential difference vary greatly with each type of cell. Moreover, cells of the same type and same model vary in physical properties depending on the production lot. Even the cells in the same production lot cannot be connected in parallel unless their conditions are controlled strictly. Thus, combining multiple cells into a battery block must be done carefully by strictly controlling the charge/discharge characteristics of each cell.
The overall life of an intelligent battery pack depends on the life of the battery block. When battery block performance degrades, the performance of the intelligent battery pack degrades. Battery packs whose life has expired such as by exceeding a prescribed charge/discharge count should be collected and recycled, or disposed of after being rendered harmless, by the vendors that have manufactured or sold the battery packs. In particular, the lithium cobalt oxide used for positive poles of lithium ion batteries contains cobalt, which is a rare metal and is toxic to humans. Thus, the batteries must be recycled appropriately.
Because of the expense of replacing a degraded intelligent battery pack, there are dealers who try to reuse intelligent battery packs by replacing only the battery blocks. The act of making alterations to genuine battery packs and reselling the altered battery packs is regarded herein as an inauthentic act. The characteristics of the cells in inauthentically recycled battery blocks are not always matched. In addition, the battery blocks used in battery packs recycled inauthentically sometimes have defects such as small package-wall thickness, insufficient sealing of contents, nonuniform composition of the contents, and large amounts of impurities in the contents. As a result, the inauthentically recycled battery pack may ignite, fume, or burst, causing a fire or damage in the electronic equipment. Thus, the battery blocks in battery packs should be replaced only by authentic manufacturers that possess sufficient manufacturing expertise to insure the safety of the remanufactured battery pack.